Which material can be used as backfill outside a foundation without being compacted?

• A. Controlled low strength material
• B. Gravel
• C. Compacted soil
• D. Concrete

Answer: (A)

Controlled low strength material (CLSM) is the correct choice for backfill outside a foundation without the need for compaction. It is specifically designed to flow easily and fill voids, providing a stable support for structures. The material is often utilized in construction because it can achieve a strength suitable for backfill while allowing for minimal or no compaction.

CLSM usually consists of a mixture of cement, water, and aggregates, and has a lower density compared to traditional concrete. This property allows it to be placed easily around foundation elements without requiring mechanical compaction, which can reduce labor costs and improve construction efficiency.

Using gravel, while it can provide good drainage and support, typically requires compaction to achieve the desired density and stability. Similarly, compacted soil and concrete are not suitable for placement without compaction; compacted soil requires careful handling to ensure proper load-bearing capacity, while concrete must be properly placed and cured to avoid issues like cracking or insufficient strength.

Thus, the unique properties of CLSM make it particularly advantageous for backfilling applications where ease of placement and sufficient structural support are necessary without the complications of compaction.